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Date: Mon, 25 Sep 2023 09:29:40 +0200
From: AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com>
To: Nícolas F. R. A. Prado
<nfraprado@...labora.com>,
"Rafael J . Wysocki" <rafael@...nel.org>,
Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: kernel@...labora.com, Amit Kucheria <amitk@...nel.org>,
Caesar Wang <wxt@...k-chips.com>,
Eduardo Valentin <edubezval@...il.com>,
Javi Merino <javi.merino@...nel.org>,
Sascha Hauer <s.hauer@...gutronix.de>,
Zhang Rui <rui.zhang@...el.com>, linux-kernel@...r.kernel.org,
linux-pm@...r.kernel.org
Subject: Re: [PATCH v2] thermal/core: Don't update trip points inside the
hysteresis range
Il 22/09/23 20:44, Nícolas F. R. A. Prado ha scritto:
> When searching for the trip points that need to be set, the nearest
> higher trip point's temperature is used for the high trip, while the
> nearest lower trip point's temperature minus the hysteresis is used for
> the low trip. The issue with this logic is that when the current
> temperature is inside a trip point's hysteresis range, both high and low
> trips will come from the same trip point. As a consequence instability
> can still occur like this:
> * the temperature rises slightly and enters the hysteresis range of a
> trip point
> * polling happens and updates the trip points to the hysteresis range
> * the temperature falls slightly, exiting the hysteresis range, crossing
> the trip point and triggering an IRQ, the trip points are updated
> * repeat
>
> So even though the current hysteresis implementation prevents
> instability from happening due to IRQs triggering on the same
> temperature value, both ways, it doesn't prevent it from happening due
> to an IRQ on one way and polling on the other.
>
> To properly implement a hysteresis behavior, when inside the hysteresis
> range, don't update the trip points. This way, the previously set trip
> points will stay in effect, which will in a way remember the previous
> state (if the temperature signal came from above or below the range) and
> therefore have the right trip point already set. The exception is if
> there was no previous trip point set, in which case a previous state
> doesn't exist, and so it's sensible to allow the hysteresis range as
> trip points.
>
> The following logs show the current behavior when running on a real
> machine:
>
> [ 202.524658] thermal thermal_zone0: new temperature boundaries: -2147483647 < x < 40000
> 203.562817: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=36986 temp=37979
> [ 203.562845] thermal thermal_zone0: new temperature boundaries: 37000 < x < 40000
> 204.176059: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=37979 temp=40028
> [ 204.176089] thermal thermal_zone0: new temperature boundaries: 37000 < x < 100000
> 205.226813: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=40028 temp=38652
> [ 205.226842] thermal thermal_zone0: new temperature boundaries: 37000 < x < 40000
>
> And with this patch applied:
>
> [ 184.933415] thermal thermal_zone0: new temperature boundaries: -2147483647 < x < 40000
> 185.981182: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=36986 temp=37872
> 186.744685: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=37872 temp=40058
> [ 186.744716] thermal thermal_zone0: new temperature boundaries: 37000 < x < 100000
> 187.773284: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=40058 temp=38698
>
> Fixes: 060c034a9741 ("thermal: Add support for hardware-tracked trip points")
> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>
> ---
>
> Changes in v2:
> - Changed logic as suggested by Rafael
> - Added log example to commit message
> - Added fixes tag
>
> drivers/thermal/thermal_trip.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/thermal/thermal_trip.c b/drivers/thermal/thermal_trip.c
> index 024e2e365a26..597ac4144e33 100644
> --- a/drivers/thermal/thermal_trip.c
> +++ b/drivers/thermal/thermal_trip.c
> @@ -55,6 +55,7 @@ void __thermal_zone_set_trips(struct thermal_zone_device *tz)
> {
> struct thermal_trip trip;
> int low = -INT_MAX, high = INT_MAX;
> + bool same_trip = false;
> int i, ret;
>
> lockdep_assert_held(&tz->lock);
> @@ -63,6 +64,7 @@ void __thermal_zone_set_trips(struct thermal_zone_device *tz)
> return;
>
> for (i = 0; i < tz->num_trips; i++) {
> + bool low_set = false;
> int trip_low;
>
> ret = __thermal_zone_get_trip(tz, i , &trip);
> @@ -71,18 +73,31 @@ void __thermal_zone_set_trips(struct thermal_zone_device *tz)
>
> trip_low = trip.temperature - trip.hysteresis;
>
> - if (trip_low < tz->temperature && trip_low > low)
> + if (trip_low < tz->temperature && trip_low > low) {
> low = trip_low;
> + low_set = true;
> + same_trip = false;
> + }
>
> if (trip.temperature > tz->temperature &&
> - trip.temperature < high)
> + trip.temperature < high) {
> high = trip.temperature;
> + same_trip = low_set;
> + }
> }
>
> /* No need to change trip points */
> if (tz->prev_low_trip == low && tz->prev_high_trip == high)
> return;
>
> + /*
> + * If "high" and "low" are the same, skip the change unless this is the
> + * first time.
> + */
> + if (same_trip && (tz->prev_low_trip != -INT_MAX ||
> + tz->prev_high_trip != INT_MAX))
> + return;
> +
> tz->prev_low_trip = low;
> tz->prev_high_trip = high;
>
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